Geofex Sypder, noisy PSU problem

[stompystomp]

I have built a PSU to power my RM with. Problem is, when I power it of a battery it hisses far less than off the PSU. I used the spyder schematic. Using a 7809 voltage regulator.

So I have the output from my transformer 12V (toroiodal) into a W005 (bridge rectifier). Then between the + an 0v goes a 1000uF 35V, then the + goes into pin 1 of the voltage reg. Pin 2 to ground. Then I connect a 10uF 16V cap between pin 3 and pin 2(ground) and then I power my RM off that point.

It doesn't hum (not mains hum). It is just really hissy- seems to amplify the background noise. When I turn the power off to the PSU the hiss slowly goes away then quiet, then it quickly build back up again then slowly dies away. I.e Twice!!! is this normal?

I have built PSU's in the past (many moons ago), and they worked fine. Not sure how and why this one is injecting noise into the circuit.

Any help would be much appreciated.

Stompy.

[R.G.]

Your power supply is most likely oscillating. Hook 0.01uF ceramic caps at both input to ground pin and output to ground pin and see if it goes away.

[stompystomp]

Thanks RG, no luck I'm afraid though.

Attached 10nF between pin 1 and 2 then another one between 3 and 2. Still the same with out without them.

I have recorded an audio clip.

http://www5.upload2.net/download/XfU1oBib1knjdrm/psu+noise.mp3

Starts with the RM running off batteries. Then I have spliced in a clip with exactly the same levels and mic positioning of it running off the PSU., then back again. You should get some idea of the noise level I am talking about.

Here is my PCB design. Fairly simple and looks ok to me.

http://www5.upload2.net/download/RT7CKk4TmU5z48Q/psuboard.jpg

Really stumped with this one. Using a toroidal transformer. Secondary goes to the AC IN part (transformer is 12v AC output). Then the +9 and Ov points go to my RM, and it's causing the hiss/ extra noise heard. The measured voltage at the +9v 0v point is 8.95v DC which I think looks fine.

Over to you guys for some more hints/tips!

Stompy.

[R.G.]

That's very strange. When a power supply induces hiss, especially a prominent, "angry-sounding" hiss, it's usually the audio result of radio-frequency oscillation.  I was guessing that the regulator was oscillating, which they do under some conditions if not well-decoupled.

Given that, is there any power decoupling inside the pedal?

[stompystomp]

I have built the rangemaster circuit as found in the Geofex Rangemaster pdf project file. (Not sure what power decoupling means )

[R.G.]

No problem. Decoupling as I used the term means some capacitance across the +9v-to-ground inside the pedal. What this does is establish a low impedance path between +9V and ground so that any sudden pulses of current the circuit needs are supplied from the local capacitor, instead of having to travel through the (presumably long) wires to the power supply regulator.

I would use 22uF electrolytic and 0.1uFceramic in parallel inside the unit. It's been so long since I wrote the Rangemaster stuff that I can't remember if I put one in there or not.

[stompystomp]

Thankyou RG. That seems to have fixed the excessive noise issue very well. now there is little difference between running it off batteries or off the PSU. One problem though (never that simple). With the guitar volume rolled fully off, the Output is as expected but when I turn it up, it starts picking up noise (dreaded hum noise!) I have tried it on both my guitars and both do the same. On my les paul if I roll the tone off it nearly all goes away. Is this mains hum I can hear? The PSU box is earthed so not sure what else I can do.

Any thoughts.

Stompstomp

[R.G.]

Great! We're making progress.

This problem was, of course, always there, just masked by the other problems. It's very much like peeling an onion in layers - you take off one layer, and it reveals another layer that makes you cry. 

Although you don't say, presumably it does not hum at max volume on batteries.

A low hum is either mains hum or rectifier ripple. Rectifier ripple is double the mains frequency in full wave rectified cases like yours. It's not easy to pick out which these it is by ear, but some people can do it. You say "mains" so I'm guessing that you're in some place other than the USA and have 50 Hz power, not 60 Hz like we have here. Give a careful listen and see if you can tell the difference between 50Hz and 100Hz. 100Hz is about halfway between three and four frets up from low E in standard tuning. 50 Hz is an octave lower.

Can you tell?